Effective and Low-Cost In Situ Surface Engineering Strategy to Enhance the Interface Stability of an Ultrahigh Ni-Rich NCMA Cathode.

Ultrahigh Ni-rich quaternary layered oxides LiNi 1- x - y - z Co x Mn y Al z O 2 (1 - x - y - z ≥ 0.9) are regarded as some of the most promising cathode candidates for lithium-ion batteries (LIBs) because of their high energy density and low cost. However, poor rate capacity and cycling performance severely limit their further commercial applications. Herein, an in situ coating strategy is developed to construct a uniform LiAlO 2 layer. The NH 4 HCO 3 solution is added to a NaAlO 2 solution to form a weak alkaline condition, which can reduce the hydrolysis rate of NaAlO 2 , thus enabling uniform deposition of Al(OH) 3 on the surface of a Ni 0.9 Co 0.07 Mn 0.01 Al 0.02 (OH) 2 (NCMA) precursor. The LiAlO 2 -coated samples show enhanced cycling stability and rate capacity. The capacity retention of NCMA increases from 70.7% to 88.3% after 100 cycles at 1 C with an optimized LiAlO 2 coating amount of 3 wt %. Moreover, the 3 wt % LiAlO 2 -coated sample also delivers a better rate capacity of 162 mAh g -1 at 5 C, while that of an uncoated sample is only 144 mAh g -1 . Such a large improvement of the electrochemical performance should be attributed to the fact that a uniform LiAlO 2 coating relieves harmful interfacial parasitic reactions and stabilizes the interface structure. Therefore, this in situ coating approach is a viable idea for the design of higher-energy-density cathode materials.